The hydrodynamic bearing is dependent on rotation and a low pressure oil supply to build up a wedge of oil between two surfaces – the shaft and bearing – to create the oil film producing the load support. The geometry of the bearing surfaces aid in forming the wedge. A low pressure oil source is required. Spindles built with hydrodynamic bearings feature extreme accuracy, and very good vibration dampening. High loads at start-up should be avoided.
The advantages of the fluid fed bearings, as outlined, outweigh the increased costs. Spindles built with fluid fed bearings are more expensive to build. This is mainly due to low volume, the unique geometry of the bearings and the additional processing necessary to ensure the precision.
Either style of fluid bearing dictates the need for an auxiliary temperature controlled oil supply system. High pressure oil supply systems are needed for the hydrostatic bearing while low pressure oil systems are used for hydrodynamic bearings.
Because both types of fluid fed bearings are utilized in precise applications, temperature control for the oil supply system is a necessity. Oil filtration, generally in the range of 1-micron is also required. An accumulator in the oil supply system is recommended so that oil pressure can be maintained during shutdown in the event of a power failure.
When maintained as directed, spindles with fluid fed bearings can provide infinite (in theory) bearing life since there is no metal to metal contact. Failures are usually due to human error such as poor maintenance of the oil filtration, use of improper fluid viscosity, temperature control system failures, and machine crashes.